Assembling customized sensor arrays on structures by direct-ink-writing for real-time complex crack monitoring

Crack growth is a primary failure mechanism in engineering structures, and its real-time monitoring is critical for reliable damage evaluation and life prediction. In this study, a customizable crack monitoring sensor array is developed using direct ink writing (DIW) technology. The sensing concept translates crack-induced mechanical rupture into discrete, stepwise resistance variations, providing a direct and unambiguous electrical signature of crack initiation and propagation in real time. Here, the real-time capability refers to the synchronous electrical response triggered by fracture events, rather than high-speed temporal resolution. Owing to the high design flexibility of DIW, the sensor architecture can be readily tailored in terms of geometry, signal response, and system integration. Experimental validation demonstrates the capability of the proposed sensor to monitor multiple crack modes, including quasi-static fracture, dynamically unstable brittle fracture, fatigue crack growth, and crack-path deflection, across different substrate materials. The results highlight the effectiveness of the DIW-fabricated sensor array as a versatile and scalable platform for event-based, multi-mode crack monitoring in structural health monitoring applications.